Many printing machines accomplish lead edge register of paper sheets at the impression cylinder clamp or gripper by forcing the leading edge of the sheet into the stops of the open gripper and buckling it. This is accomplished by feed rollers which grip a sheet and accelerate it into the gripper. Lateral edge or side registration of the sheet is also desirable. Short-coupled sheet feed systems, ones exemplified by vacuum pick-up and delivery of sheets from the stack to forwarding rollers which accelerate the sheet lead edge into the impression cylinder grippers, either have minimal side registration between the impression cylinder and the pile or are completely without it. The prior art has attempted to overcome the sheet side registration deficiencies by interposing conveyor boards or transport tables between the sheet stack and the impression cylinder grippers. However, these have stopped the sheet to align it before advancing the lead edge thereof into the impression cylinder grippers.
All modern press/duplicator feeding devices with a conveyor board have head lay stops and side lay stops. The side guiding is done by means of push or pull guiding devices and the head lay or lead paper edge registration is done by two or more registration stops. This is known in the industry as three points registration. When handling paper at higher speed rates such as 5,000 I.P.H. (impressions per hour) and above, it has been noticed that the regular and heavy paper stocks sometimes bounce from the head lays two to four times before settling down. Only after that can the sheet of paper be pushed or pulled to the side for good side registration. The process of paper settling at the head lays takes a substantial amount of the printing cycle and after being side guided the paper sheet accelerates toward the grippers of the impression cylinder.
When handling light paper stocks the problem is even more difficult. The light-weight paper tends to create an accordion shape and creases when fed into the head lays at high printing speed. As a result, presses cannot feed light-weight papers at high speed and in order to be safe the printing speed is reduced. That, in turn, reduces the productivity of the press. Introduction of stream feed with a conveyor board improved the dynamics of the paper handling and registration because the speed of the paper on the conveyor board was reduced by the ratio 4/1 or 5/1. But even under these conditions, such light-weight paper sometimes buckles or creases as it contacts the front stops when the machine is operating at high printing speeds.
To solve the problem, a preferred embodiment of the present invention uses a transport table of a type customarily used to feed paper stock on a folding machine to transport the paper sheets from the paper stack to the feed rollers which transfer the sheets to the impression cylinder. The modifications made to the standard table achieve the synchronization of the operation of the sheet transport belt of the table and its sheet pickup (i.e., a vacuum suction device) with the operation of the offset duplicator feed rollers and the impression cylinder.
In a preferred embodiment of the present invention, the impression cylinder, the drive mechanism for the transport table and the vacuum device are all geared together to achieve the desired synchronization. Sensors note the instantaneous position of the impression cylinder and the instantaneous position of the paper sheets being carried by the transport belt. By utilizing a microprocessor to compare the instantaneous position of the paper on the transport board with the instantaneous rotated position of the impression cylinder, the computer can generate an error signal if the paper is not in a position at the speed at which it is traveling to arrive at the proper time in the gripper of the impression cylinder. This error signal is coupled to the vacuum device that is picking up the paper sheets from the paper stack and transferring them to the transport belt. By varying the time at which the suction is turned on, the time at which the paper is deposited on the transport belt may be delayed or advanced to change the instantaneous position of the paper on the transport belt with respect to the instantaneous rotary position of the impression cylinder gripper. Thus, accurate timing is achieved for the arrival of the paper at the gripper of the cylinder.
In an alternate embodiment of this invention, synchronization of timing of paper arrival at the cylinder gripper is achieved by varying the speed of the transport belt or the forwarding rollers in order to compensate for any mispositioning or buckling of the paper in the transport of the paper to the grippers.
Thus, in accordance with this improved and novel invention, paper is allowed to move continuously through the machine without stopping or starting and thus increases the output of the machine substantially over its present maximum capability.
Accordingly, it is an object of the present invention to provide a printing or duplicating machine in which the paper moves continuously from the paper stack to the impression cylinder without stopping or starting.
It is another object of the present invention to detect the instantaneous position of the paper on the transport belt with respect to the instantaneous rotated rotary position of the impression cylinder gripper so that it can be determined if the paper sheet is at the right position to be advanced into the gripper of the impression cylinder at the proper time.
It is also an object of the present invention to utilize a microprocessor to generate an error signal when the instantaneous position of a sheet of paper on the transport belt is incorrect with respect to the instantaneous rotary position of the impression cylinder gripper and to utilize the error signal to control the application of vacuum to the vacuum device which removes the individual paper sheets from the paper stack and transfers them to the transport belt, and thus vary the position of the paper on the transport belt such that the error signal is removed.